Bioplastic using a plant as a raw material can contribute to a countermeasure against petroleum depletion and global warming, and has been started being used not only in common products such as packaging, containers and fibers but also in durable products such as electronics and automobiles.
However, general bioplastics, such as polylactic acid, polyhydroxyalkanoate and modified starch, all use starch materials, more precisely, edible parts, as raw materials. Accordingly, for fear of future food shortage, it has been desired to develop a novel bioplastic using a non-edible part as a raw material.
As bioplastic using a non-edible part as a raw material, various types of bioplastics using cellulose, which is a main component of non-edible parts of wood and plant, have been already developed and commercialized.
Cellulose is a high molecular weight compound formed by polymerization of β-glucose. Since cellulose has high crystallinity, it is hard, fragile and absent of thermoplasticity. In addition, since cellulose contains many hydroxy groups, water absorbability is high and water resistance is low. Then, various investigations have been made to improve the properties of cellulose.
For example, Patent Literature 1 (JP11-255801A) discloses a biodegradable graft polymer having thermoplasticity obtained by ring-opening graft polymerization of cellulose acetate having a hydroxy group with ε-caprolactone.
Meanwhile, a material using a non-edible component other than cellulose has been developed. For example, cardanol derived from cashew nutshell and rosin derived from pine resins (particularly, abietic acid as a main component), since they have stable amount of production and excellent functionality ascribed to their characteristic molecular structures, have found various applications.
As an example of using cardanol, Patent Literature 2 (JP10-8035A) discloses a friction material for brake, which is formed of a fiber base material made of an aramid pulp and a cellulose fiber, and a filler made of calcium carbonate and cashew dust, with the use of a binder made of a phenol resin. Patent Literature 3 (JP2001-32869A) discloses a friction material formed of a base material made of an aramid fiber and a cellulose fiber, and a filler made of graphite and cashew dust, with the use of an organic-inorganic composite binder. It is described that the friction material is applied to clutch facing of a power transmission system of automobiles etc.
In Non Patent Literature 1 (George John et al., Polymer Bulletin, 22, p. 89-94 (1989)), it is described that water resistance of paper can be improved by soaking a paper sheet in cardanol to perform a grafting reaction through which cardanol binds to cellulose constituting the paper sheet. It is described that, in the grafting reaction, a terminal double bond of cardanol binds to a hydroxy group of cellulose in the presence of boron trifluoride diethyl ether (BF3—OEt2).
Meanwhile, an example of using rosin is disclosed in Patent Literature 4 (JP5-86334A) in which a reaction product obtained by adding purified rosin to α,β-unsaturated monocarboxylic acid and/or an α,β-unsaturated dicarboxylic acid is hydrogenated to obtain a colorless rosin derivative, which is suitable as a pigment coating agent, a sizing agent for manufacturing paper, a flux agent, etc.
Patent Literature 5 (JP6-33395A) discloses that an esterified reaction product obtained by reaction of rosin, a polyol, a polyvalent (trivalent or more) carboxylic acids or an anhydride thereof, and an α,β-unsaturated polybasic acid is used as a sizing agent component.
Non Patent Literature 2 (Muhammad A. Hussain, Journal of Polymer Science: Part A: Polymer Chemistry, 46, p. 747-752 (2008)) describes a hydroxypropyl cellulose derivative to which abietic acid is bound by grafting and that since this derivative has a property of swelling with water and an organic solvent, it is possibly used in sustained-release preparations.